From 1925, a model triscaph
I love it! Thanks Aerohydro. It is so simple. WIth a triangular deck to sit on there will be no racking of the structure and being suspended on three points (hulls) no torsional forces can be induced into the structure. I think it could be built incredibly light.
Very similar to an iceboat in many ways, I suppose, yet I never saw its potential. Same goes for triscaph craft. I wonder why that is?
Well that’s taken care of my thinking time for the rest of the afternoon 😊
James
But if you begin to fly the windward float, how well does the tail float and that long connecting beam react to the upward force?
But if you begin to fly the windward float, how well does the tail float
It will float lower in the water as the weight will be borne by two ‘hulls’ now instead of three. It would be prudent to design for this eventuality
and that long connecting beam react to the upward force?
It will presumably bend some as the bending moment increases. Again, it would be prudent to design for this. There would still be no torsional forces present. Imagine e three legged stool. It cannot rock or distort its shape whether resting on three or two legs. Only on four legs (or two long hulls) does this happen and needs to be braced against adding weight which in turn needs to be supported!
Like a three wheeler car, I imagine best results would come from widely spacing the three hulls and positioning the majority of the weight (CoG) close to the paired forward hulls. Perhaps a cockpit/shelter that was triangular shaped would work best structurally and dynamically.
By extending the rearward hull, you would increase stability and increase turning moment when the rear hull is steered as a rudder. I think the hulls would need to fold to take advantage of a wide ‘footprint’ and make a contraption like this practical to trailer and launch. It could be done, of course, but not sure how best to do it.
When i look at a stool compared to this triscaph i can’t help but wonder if the triscaph’s crossbeams w/ tailbeam set-up could be anywhere near as stiff as a stool’s triangular beams connecting all three legs usually below the center of the stool’s height, in addition to the top of the three legs all connected to the bottom of the seat as well.
good question. However, I introduced the three legged stool as an analogy not as an argument. I was not comparing the stool with the triscaph but rather the three legged stool compared to a four legged stool and the triscaph compared to a catamaran, for instance.
The only feature and similarity I was intending to highlight between the stool and the triscaph was simply the three contact patches versus four for the benefit of showing (hopefully) that three contact patches eliminate the introduction of torsional forces. Nothing more 😊
The model as drawn would be prone to racking forces as there is no triangulation in the structure. And there are the ever present beam forces to deal with. Any serious design would have to deal with these, of course.
What fired my interest was that it was different 😊 ;
that it was also similar in some ways to a proa in that a proa could be envisaged as having three points of contact (either end of the vaka and the ama being the third point);
that it would not require engineering to overcome torsional forces (as I have mentioned);
that it probably may not require rocker to be designed into the hulls/floats/amas; and
that it might steer very well using the rear float and yet have very shallow draft.
Perhaps the rear float could have an end-plate to compensate for lack of draft. Perhaps all three floats could be designed as shallow flat bottomed foils with or without endplates (chine runners)
Thanks James,
i continued with your stool analogy only in the hope that you might elaborate on the following:
The model as drawn would be prone to racking forces as there is no triangulation in the structure. And there are the ever present beam forces to deal with. Any serious design would have to deal with these, of course.
considering those racking forces, in your opinion, could a back-yard, diy, builder on a budget design and engineer an off-shore triscaph ?
i can only imagine that the racking forces would try to tear an off-shore triscaph apart.
Red ceder, yes I think it is entirely possible design-wise. You may need help with the engineering depending on your level of knowledge and expertise.
If you join the three hulls with a perimeter beam forming a large triangle, that will eliminate the racking forces.
To manage the bending forces on the beams, you need to go for depth with the beams being deepest in the middle and tapering towards their ends.
The ultimate structural answer is to construct a three sided pyramid on top of the triangular perimeter beam so that you now have a tetrahedron - the strongest and most efficient (materials-wise) structure there is.
The aesthetics and ergonomics may need a little development though 😊
Here’s a recently built full-sized triscaph. This is the Windspider, designed in the 1990s by Pietro Terzi of Italy. There were prototypes as well as a pre-production model. Note that the hulls are inflatable and that there’s a centre fin and a pair of rudders:
PietroTerzi.com - Windspider (a photo gallery, loads slowly)
Cheers,
Paul
Not speaking from first-hand personal experience, though I’ve been near a number of triscaphs…
Though many have been built, generally, triscaphs aren’t successful. There are notable exceptions (Yellow Pages Endeavor, for instance), but generally, not successful.
Hydrodynamically, their hulls are usually short and fat. Unless specifically designed as planing hulls (YPE, several successful Weymouth speedsters) they are too fat, too short and their wave systems are too tough to climb out from. “Displacement speed” on an 8’ hull is about 4 kts…
Multiple bows and sterns; there is a drag penalty for ending or beginning a hull in the water (how’s that for scientific?) It’s best do it as seldom as possible.
Third, structure. Most sailboats use the stiffness of their hulls as a part of the structural rigidity of the entire platform. Triscaphs don’t, which means that no matter how “efficient” the triangulation may be, you’re still carrying un-uilized structural stiffness (the hulls), so are duplicating systems to get that rigidity—with commensurate weight and cost penalties.
IMO, development into making hulls of “ordinary” cats, tris and proas pivoting in order to reduce wracking strains are more likely to bear fruit than triscaphs, but to every Jack, his Jill. 😉
Dave